It is common to take small samples from a product flowing through a pipeline and to accumulate the individual samples, over time, in a sample cylinder. The samples are typically pumped into the sample cylinder under pressure at a sample station. When the sample cylinder is full or nearly full of the samples, the cylinder is typically removed from the pump and associated piping at the sample station and taken to a laboratory for analysis of the collective sample. In many cases, the sample station is located in a rural area and the laboratory is located in a city. It therefore becomes important for operators to be able to quickly change out a full sample cylinder with an empty sample cylinder as the operator goes from sample station to sample station.
It has therefore become common for sample cylinders to be connected to the piping system at a sample station with a flexible line and a quick-connect. When the sample cylinder is full, the samples are under pressure that may range widely from about 5 psi to about 5,000 psi. The quick-connect that is connected to the sample cylinder will be rated for the maximum pressure experienced by the piping system and the cylinder; however, when disconnected, the pressure rating for many quick-connects is substantially less than the connected rating. There is a need for an inexpensive bleeder valve in the piping system to depressurize the fluid in the quick-connect between the sample cylinder shut-off valve and the shut-off valve in the piping system before the quick-connect is disconnected to switch out the full sample cylinder with an empty sample cylinder. Such an inexpensive bleeder valve could be opened to release the pressure in the quick-connect to a level at or below the rated pressure of the quick-connect in the disconnected mode.
In some applications, the sample may contain hazardous fluids like hydrogen sulfide or chlorine. If some of the hazardous pressurized fluid is vented in the proximity of the operator, it could be hazardous to their health. In these situations, there is a need for an inexpensive bleeder valve that is also resistant to the hazardous materials to release the pressure and direct the vented fluid to a flare or other disposal location. For example, if natural gas is the process fluid that is being sampled, and there is some hydrogen sulfide in the gas, the inexpensive bleeder valve and the seals need to be made from a material that resists the corrosion and other deleterious effects of the hydrogen sulfide.